1. Field of the Invention
This invention relates to a method and apparatus for regenerating wet activated carbon containing adsorbed volatile organic adsorbate and more particularly to a method and apparatus involving sequential treatment with low pressure steam and vacuum to achieve effective regeneration.
2. Description of the Prior Art
Activated carbon is employed as an adsorbent for removing selected ingredients from a fluid (gas or liquid) in which the ingredients are carried as a minor component. The effectiveness of activated carbon in removing selected ingredients decreases as the adsorbed quantity of the ingredient increases. The phrase "spent activated carbon" herein refers to activated carbon with a lowered effectiveness resulting from its adsorbed adsorbate. The "spent activated carbon" may be restored to greater effectiveness through regeneration. The activated carbon containing adsorbate may be regenerated to desorb the adsorbed ingredient whereby the adsorption effectiveness of the regenerated activated carbon approaches that of fresh activated carbon. Regeneration typically occurs by heating in air or in steam or inert gases and by vacuum treatment. Heating in air or any sort of oxidizing atmosphere causes some combustion of the activated carbon and a corresponding increase in the size of the pores of the activated carbon where adsorption occurs. As a result the heat-regenerated activated carbon has a lowered attainable effectiveness. Steam regeneration is effective in removing only a portion of the adsorbed volatile organic adsorbate and leaves behind within the pores of the activated carbon a substantial amount of the adsorbed volatile organic adsorbate which precludes restoration of the initial adsorption effectiveness of the activated carbon. Vacuum treatment of wet activated carbon containing adsorbed organic volatile adsorbate is ineffective because of the need to volatilize the water of the wet activated carbon as well as the adsorbed volatile organic adsorbate.